Out of roughly 8 attempts, we have only received 2 traces that look as they should (see attached 20080726-shot 3 txt.txt file) and the other 6 were garbage (see attached 20080726-0001.txt file). The data in the good trace is about (with only slight variations) what we would expect to see every time. The numbers in the table have been converted to PSI with a custom probe setting; 0.25V = 0 PSI and 4.25V = 150 PSI. Our trigger point is for probe B at 1V (~28 PSI), yet (as you can read) in the garbage trace we never saw above 1.1 PSI.

My questions are as follows:

-Why does the waveform not pass through the trigger point? It would make sense to me to see a plot of 1V (~28 PSI) for probe B at time ZERO.
-Do we have a problem triggering? Why are we getting these garbage traces?
-Any other suggestions?

Any light you can help shine would be greatly appreciated. Thank you in advance.

Could this have anything to do with the resolution enhancement feature? There are several warnings about it in the help file, with such ominous words as "flat line" (the "bad traces" are almost that), but it doesn't give a whole lot of guidance except to try different amounts of resolution enhancement.

Examination of your files indicate that the behaviour in your application is due to the trigger hysteresis level of the PS2203.

The choices are to increase the trigger threshold to around a minimum of 12 counts above the level of the dip in the trigger waveform (around 32 PSI?) or, upgrade to the PS2205 which supports advanced triggers.

Any explanation as to why the waveform never pass through the trigger diamond?

I will e-mail a couple other psdata files to you of other "good" traces from when we were figuring out the best trigger settings. I use the word "good" loosely as we had good numbers but improper trigger settings (you'll noticed it captured the rising pressures before the steep rises as seen in the previously emailed psdata files). They didn't capture what we were looking for and triggered early.

What does "12 counts above the level of the dip in the trigger waveform" mean? Is this 12 of the 256 count range of the 8-bit 2203 scope? And what is the significance of the "dip" in the trigger waveform?

Another question - how was it determined that this is a trigger hysteresis problem? I ask because the "bad trace" captured never exceeded about 1 psi (0.28 VDC) anywhere in the trace. The trigger level was set at 28 psi (1 VDC). With the scope set at -2 to +2 VDC, the trigger setpoint is 18% of the scope's range above the highest measured signal, or about 46 counts on an 8 bit scope. Yet it still triggered.

In the distant past (but within the last 5 or 6 years) I've had difficulties with erratic triggering (ADC40, ADC11/10) that seemed to have been fixed, at times, by NOT using a custom range, that is, just staying with the straight voltage range and converting the data in a spreadsheet.

Iâ€™ve noticed that you are applying a full 4-bits of resolution enhancement which will have a significant low-pass filtering effect on the displayed signal. Further, it is highly probable that the scope is triggering on an area (such as spike) that is removed from the displayed signal as a result of the filtering.

My assessment from your 'good trace' is that you require a trigger level of 30-31 psi for reliable triggering, and that is due to the interaction of your waveform with respect to the PS2203 trigger hysteresis of 6-7 psi (10-12 LSB).

NOTE for Hillp:
Thank you for your comments, however, I would ask that you start a new thread or submit an email to our helpdesk ([url]support@picotech.com[/url]) as it is quite difficult to address two customers with diverging issues. As my prime aim is to resolve the initial problem presented by Alex, I thank you in advance for your understanding.

Sorry, Picojohn, that I wasn't clear enough in my questions to make it evident that I was addressing this current topic. I'll try again:

RE: resolution enhancement
Thanks for the tip on the resolution enhancement; we'll take this out completely and see what the traces show. Are there any tips on how much we can use? The events we're capturing are not very easily generated; they are one-shot DC voltage patterns, not a repetetive signal at all. Of course we will keep ETS off in any case.

RE: triggering
Is there any place I could educate myself on the details of the PS6 triggering mechanism and its hysteresis? I know what hysteresis is in electromechanical systems, like a knob on a potentiometer that slips a little before it turns the shaft, thus leading to different resistance on the pot for the same knob position, depending on the direction the knob was last turned. I think I learned from your latest post that the displayed trace after triggering is not the same as the data used to trigger the scope, at least with resolution enhancement operational. The hysteresis and advanced triggering writeups in the PS6 help file talk about a hysteresis trigger feature in advanced triggering, but not about normal triggering and how it works with regards to the amount of signal movement necessary to trigger. This may become important as we substitute other pressure transducers (such as 0-25 mV output over 0-50 psi) and adjust the scope range to compensate, thus changing the number of counts/psi.

My comment about not using custom ranges in earlier versions of Picoscope was meant to ask if the range conversion from volts to psi should have any effect on triggering reliability. I did notice in PS6 that the trigger level is still specified in volts, even though the signal is being displayed in psi per our setup.

The trigger level that I set in the trigger boxes (for instance 1 volt rising edge) arms the trigger when the signal reaches it (1 volt), and then the trigger actually fires when the signal reaches 10 least significant bits above the trigger level? This would be at 1.156 volts for a chosen range of -2 to +2 VDC. (4 volts range over 256 least significant bits gives 15.6 mV/LSB. 10 of these is 156 mV.)